An electronic device may include one or more circuit boards. A typical circuit board is a two-dimensional (2D) planar board that mechanically supports electronic components. The electronic components may comprise, for example, resistors, capacitors, switches, batteries, and other more complex integrated circuit components, i.e. microprocessors. The circuit board typically comprises a dielectric material, for example, a plastic material.
The circuit board may include conductive traces on the surface for connecting the electronic components to each other. As electronic circuitry has become more complex, multilayer circuit boards with at least two electrically conductive pattern layers have been developed. Typically, the different conductive trace layers of a multilayer circuit board may be connected through vertically extending vias, which comprise conductive materials, for example, metal. A typical multilayer circuit board may comprise a plurality of core layers with bonding layers therebetween affixing the adjacent core layers together. Each core layer typically includes a dielectric layer with electrically conductive pattern layers on the opposing surfaces of the dielectric layer. Typically, during manufacture of the multilayer circuit boards, the core and bonding layers are stacked together and then heated (laminated) to cause the bonding layer to affix the adjacent core layers together.
Even with the advent of the multilayer circuit board, as the mounted circuitry has become even more complex, the size of the circuit board and associated packaging has also increased. This increase in size may pose installation drawbacks in applications where space may be limited or where fitting a planar two-dimensional circuit board may be problematic. Three-dimensional (3D) circuit boards are an approach to this drawback of typical 2D planar circuit boards. As with the typical planar multilayer circuit board, the typical 3D circuit board may comprise a plurality of core layers with bonding layers therebetween affixing adjacent layers together.
Advantageously, 3D circuit boards may perform functions beyond the traditional mechanical support and electrical connection functions of the 2D circuit board. In other words, the 3D circuit board may be a multifunctional structure. For example, the 3D circuit board may perform mechanical, aerodynamic, and encapsulation functions.
Another approach to growth in circuit board size is integrating external electronic components into the circuit board, for example, batteries, and switches. For example, U.S. Pat. No. 7,045,246 to Simburger et al. discloses a thin film battery embedded in a multilayer thin film flexible circuit board. The circuit board comprises polyimide material, which may have some undesirable material characteristics.
One method to forming 3D circuit boards is disclosed in U.S. patent application Ser. No. 11/695,685 to Shacklette et al., also assigned to the assignee of the present invention, which is incorporated in its entirety by reference. The method includes thermoforming core layers individually on a 3D mold structure, stacking the thermoformed core layers, and laminating the stacked thermoformed layers at even a greater temperature. One possible drawback of this method is the two-step heating and cooling process increases manufacturing time and limits productivity.